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x86/decompressor: Call trampoline as a normal function

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Move the long return to switch to 32-bit mode into the trampoline code
so it can be called as an ordinary function. This will allow it to be
called directly from C code in a subsequent patch.

While at it, reorganize the code somewhat to keep the prologue and
epilogue of the function together, making the code a bit easier to
follow. Also, given that the trampoline is now entered in 64-bit mode, a
simple RIP-relative reference can be used to take the address of the
exit point.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Link: https://lore.kernel.org/r/20230807162720.545787-10-ardb@kernel.org
This commit is contained in:
Ard Biesheuvel
2023-08-07 18:27:06 +02:00
committed by Borislav Petkov (AMD)
parent 00c6b0978e
commit e8972a76aa
2 changed files with 36 additions and 45 deletions
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2
arch/x86/boot/compressed/pgtable.h
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@@ -6,7 +6,7 @@
#define TRAMPOLINE_32BIT_PGTABLE_OFFSET 0
#define TRAMPOLINE_32BIT_CODE_OFFSET PAGE_SIZE
#define TRAMPOLINE_32BIT_CODE_SIZE 0x80
#define TRAMPOLINE_32BIT_CODE_SIZE 0xA0
#define TRAMPOLINE_32BIT_STACK_END TRAMPOLINE_32BIT_SIZE